Multimode Optical Fiber with Optimized Graded-Index Profile
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Solution Overview
Problem
Multimode optical fibers are not designed for interconnection with single-mode transmission systems, leading to modal noises that degrade transmission quality, and existing solutions either compromise modal bandwidth or require complex index profiles.
Innovation Solution
An optical fiber with a graded-index profile and optimized numerical aperture and core diameter, satisfying a specific criterion, to reduce incoherent and coherent modal noises at single-mode wavelengths while maintaining high modal bandwidth at multimode wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard multimode fiber with graded-index profile is used, then high modal bandwidth is achieved at 850 nm wavelength, but modal noises occur when connected to single-mode transmission systems at 1550 nm wavelength
Solution Approach 1:
The patent applies parameter changes by optimizing the core diameter and numerical aperture of the multimode fiber to satisfy a specific criterion C. By adjusting these parameters within defined ranges (core diameter 10-50 μm, numerical aperture 0.15-0.35), the fiber achieves compatibility with single-mode transmission systems while maintaining high modal bandwidth at 850 nm, thereby reducing modal noises at 1550 nm wavelength
Solution Approach 2:
The patent creates a universal multimode fiber that can function effectively in both traditional multimode applications (at 850 nm) and single-mode transmission systems (at 1550 nm). The optimized parameter ranges enable the fiber to support both operating wavelengths without requiring separate fiber types, achieving multi-functionality and interoperability across different transmission systems
2Object-generated harmful factors
If core diameter is reduced to minimize modal noises, then compatibility with single-mode systems improves, but modal bandwidth at multimode wavelengths decreases
Solution Approach 1:
The patent resolves this contradiction by optimizing both core diameter and numerical aperture simultaneously within specific ranges. The core diameter is set between 10-50 μm and numerical aperture between 0.15-0.35, satisfying criterion C. This coordinated parameter optimization ensures that modal noises are reduced while maintaining sufficient modal bandwidth for high-speed multimode transmission at 850 nm
3Loss of energy
If numerical aperture is increased to improve coupling efficiency, then connection losses decrease, but modal dispersion increases
Solution Approach 1:
The patent addresses this contradiction by optimizing the numerical aperture within a specific range (0.15-0.35) that balances coupling efficiency and modal dispersion. This optimized NA provides sufficient light gathering capability for low connection losses while maintaining the graded-index profile's ability to minimize modal dispersion, ensuring both efficient coupling and high bandwidth
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces modal noises at single-mode wavelengths and maintains high modal bandwidth at multimode wavelengths, enabling reliable high-speed transmission and supporting both single-mode and multimode operations.
Implementation Method 1
An optical fiber is conventionally constituted of an optical core, which transmits an optical signal, and of an optical cladding, which confines the optical signal within the optical core. To that end the refractive index of the core, nc, is greater than the one of the cladding, ng.
Implementation Method 2
The most prevalent multimode fibers in telecommunications are the refractive graded-index profile optical fibers. Such a refractive index profile guaranties, by minimizing the intermodal dispersion (i.e. the difference between the propagation delay times or group velocity of the optical modes along the optical fiber), a high modal bandwidth for a given wavelength.
Data Source
AI summary
It is proposed a home optical data network formed of an optical fiber comprising an optical core and an optical cladding surrounding the optical core, the optical core having a refractive graded-index profile with a minimal refractive index n1 and a maximal refractive index n0, said optical fiber being such that it has a numerical aperture NA and an optical core radius a satisfying a criterion C of quality of optical communications defined by the following equation:C=NA-0.02×awhere:NA=n02-n12=n0·2ΔwithΔ=n02-n122n02,Δ is the normalized refractive index difference,and in that said minimal and maximal refractive indexes n1, n0 and said optical core radius a are chosen such that NA>0.20, a>10 μm and |C|<0.20.